This invention relates to the field of opto-electronic devices and more particularly to opto-electronic devices with optical micro lenses.
Opto-electronic devices include both emitters and detectors. An opto-electronic emitter is a device that converts an electrical signal into an optical signal. Examples of opto-electronic emitters include light emitting diodes (LEDs) and vertical cavity surface emitting lasers (VCSELs). An opto-electronic detector is a device that converts an optical signal into an electrical signal. Examples of opto-electronic detectors include Charge Coupled Devices (CCDs) and resonant cavity photodetectors (RCPDs).
The development of integrated opto-electronic devices has made it possible to fabricate multiple opto-electronic devices on a single substrate to form two-dimensional arrays. These two dimensional arrays are useful in a wide variety of applications. For instance, two dimensional arrays of CCDs are often used to in digital cameras and imaging equipment, while two-dimensional arrays of VCSELs and RCPDs are often used for communication applications for switching optical signals and interfacing optical signals with electronic circuits. Techniques for fabricating and using CCDs, VCSELs, LEDs, and RCPDs are well know to those skilled in the art.
When opto-electronic devices are used in an array as emitters or detectors, an external fore lens is often employed to focus or collimate the beams of light to or from the array. Unfortunately, aberrations are often associated with the fore lens. One common aberration is a curvature of field aberration, which causes the light to be focused on a curved surface, such as a sphere, rather than on the surface of a plane. Other more complex aberrations are also common. Prior art methods for compensating for field curvature include implementing a refractive field-flatting element. Unfortunately, these refractive field-flattening elements are both costly and bulky. Therefore, a need exists for an economical and compact method for reducing the curvature of field associated with the fore lens in an optical system.
The present invention overcomes many of the disadvantages of the prior art by providing a method and apparatus for compensating for an aberration, such as a curvature of field, of a fore lens in a system that includes one or more opto-electronic devices.
In one illustrative embodiment, the present invention contemplates an optical system that includes an array of opto-electronic devices that are provided substantially in a plane. The opto-electronic devices in the array may be fabricated on the same substrate or fabricated individually and then bonded or electrically connected to a substrate to form the array. The array includes a fore optic, such as a lens, provided above the array of opto-electronic devices for collimating or focusing the light traveling to or from the array. The fore optic typically has a non-planar focal field and thus focuses or collimates the light substantially along a non-planar surface, such as a sphere or other more complex image surface, rather than along the plane of the opto-electronic devices.
To compensate for the non-planar focal field of the fore optic, an illustrative embodiment of the present invention provides a micro lens for each opto-electronic device. In this embodiment, the micro lenses are preferably substantially co-planar, with each micro lens having a focal length that varies in a manner necessary to relay or focus the opto-electronic device aperture onto the non-planar fore optic image surface. In one embodiment, the focal length of each micro lens depends on the location of the micro lenses relative to the optical axis of the fore optics.
In another illustrative embodiment, the micro lenses are not co-planar. Instead, each micro lens is separated from the fore optic (and thus a corresponding opto-electronic device) by a distance that depends on the location of the micro lens relative to the optical axis of the fore optic. By varying the separation distance between the micro lenses and the fore optic, more of the light that is focused on the non-planar focal field of the fore optic can be captured. In one embodiment, the separation distance between each micro lens and the fore optic is related to, and may track, the non-planar fore optic image surface. Each micro lens may also have a focal length that corresponds to the separation distance between the micro lens and the corresponding opto-electronic device so that the light captured by the micro lens can be effectively relayed or focused to the aperture of the corresponding opto-electronic device.
In one embodiment of the present invention, the array of opto-electronic devices are opto-electronic detectors, such as resonant cavity photo detectors (RCPDs) or charge coupled devices (CCDs). In another embodiment of the present invention, the array of opto-electronic devices are opto-electronic emitters, such as vertical cavity surface emitting lasers (VCSELs) or light emitting diodes (LEDs). In yet another embodiment of the present invention, the array of opto-electronic devices includes a combination of detectors and emitter, such as VCSELs and RCPDs.
Another illustrative embodiment of the present invention includes an optical system that has multiple opto-electronic arrays configured in a two-dimensional array on a substrate. Each opto-electronic array includes a plurality of opto-electronic devices and a corresponding fore optic provided above the opto-electronic array. Each opto-electronic array may be either centered or offset from the optical axis of the corresponding fore optic. In addition, each opto-electronic array may include emitters, detectors, or a combination of emitters and detectors.